Unified position dependent prediction combination process

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. An apparatus for video decoding includes processing circuitry that decodes prediction information for a current block in a current picture that is a part of a coded video sequence. The prediction information indicates an intra prediction direction for the current block that is one of (i) a diagonal intra prediction direction or (ii) a neighboring intra prediction direction adjacent to the diagonal intra prediction direction. The processing circuitry determines a usage of a position dependent prediction combination (PDPC) process according to the intra prediction direction of the current block. The same PDPC process is applied to both the diagonal intra prediction direction and the neighboring intra prediction direction. The processing circuitry reconstructs the current block based on the usage of the PDPC process on the current block.

INCORPORATION BY REFERENCE

This present application claims the benefit of priority to U.S.Provisional Application No. 62/859,920, “UNIFIED POSITION DEPENDENTPREDICTION COMBINATION PROCESS” filed on Jun. 11, 2019, and U.S.Provisional Application No. 62/869,015, “FURTHER UNIFICATION ON POSITIONDEPENDENT PREDICTION COMBINATION PROCESS” filed on Jun. 30, 2019, whichare incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate) of, for example, 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction of red inthe input video signal, through compression. Compression can help reducethe aforementioned bandwidth or storage space requirements, in somecases by two orders of magnitude or more. Both lossless and lossycompression, as well as a combination thereof can be employed. Losslesscompression refers to techniques where an exact copy of the originalsignal can be reconstructed from the compressed original signal. Whenusing lossy compression, the reconstructed signal may not be identicalto the original signal, but the distortion between original andreconstructed signals is small enough to make the reconstructed signaluseful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or maybe predicted itself.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and 11.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (105) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially Shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs of aneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that 11265 offers, described herein is atechnique henceforth referred to as “spatial merge.”

Referring to FIG. 1C, a current block (111) can include samples thathave been found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (112 through 116, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry.

According to aspects of the disclosure, there is provided a method forvideo decoding in a decoder. In the method, the processing circuitrydecodes prediction information for a current block in a current picturethat is a part of a coded video sequence. The prediction informationindicates an intra prediction direction for the current block that isone of (i) a diagonal intra prediction direction or (ii) a neighboringintra prediction direction adjacent to the diagonal intra predictiondirection. The processing circuitry determines a usage of a positiondependent prediction combination (PDPC) process according to the intraprediction direction of the current block. The same PDPC process isapplied to both the diagonal intra prediction direction and theneighboring intra prediction direction. The processing circuitryreconstructs the current block based on the usage of the PDPC process onthe current block.

According to aspects of the disclosure, the diagonal intra predictiondirection is one of a bottom-left intra prediction direction and atop-right intra prediction direction. In an embodiment, when thediagonal intra prediction direction is the bottom-left intra predictiondirection, a mode index of the neighboring intra prediction direction isbelow a mode index of a horizontal intra prediction direction. In anembodiment, when the diagonal intra prediction direction is thetop-right intra prediction direction, the mode index of the neighboringintra prediction direction is above a mode index of a vertical intraprediction direction.

According to aspects of the disclosure, when the intra predictiondirection is the neighboring intra prediction direction, the processingcircuitry determines whether the intra prediction direction points to afractional position. In response to a determination that the intraprediction points to the fractional position, the processing circuitrydetermines an early termination of the PDPC process.

According to aspects of the disclosure, when a current sample in thecurrent block is to be filtered by the PDPC process, the processingcircuitry determines whether a reference sample of the current sample islocated within a preset range according to a per-row or per-columnchecking. In an embodiment, the per-column checking depends on at leastone of (i) a total number of available reference samples that arelocated left to the current block, (ii) a block height of the currentblock, and (iii) a horizontal coordinate value of the current sample. Inan embodiment, the per-row checking depends on at least one of (i) atotal number of available reference samples that are located above thecurrent block, (ii) a block width of the current block, (iii) and avertical coordinate value of the current sample.

According to aspects of the disclosure, an angle of the intra predictiondirection is equal to or greater than a preset value. In an embodiment,when the intra prediction direction is closer to the vertical intraprediction direction than the horizontal intra prediction direction, theprocessing circuitry performs the PDPC process on a first number ofcolumns of samples in the current block, and the first number isdetermined according to the preset value and a block size of the currentblock. In an embodiment, when the intra prediction direction is closerto the horizontal intra prediction direction than the vertical intraprediction direction, the processing circuitry performs the PDPC processon a second number of rows of samples in the current block, and thesecond number is determined according to the preset value and the blocksize of the current block.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform any one or acombination of the methods for video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes;

FIG. 1B is an illustration of exemplary intra prediction directions;

FIG. 1C is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example;

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment;

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment;

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment;

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment;

FIG. 8A shows an illustration of exemplary intra prediction directionsand corresponding intra prediction modes in some examples (e.g., VVC);

FIG. 8B shows a table of angular intra prediction modes and theircorresponding intra prediction angles in some examples (e.g., VVC);

FIG. 9A shows exemplary weighting factors for a prediction sample at (0,0) in DC mode in accordance with an embodiment;

FIG. 9B shows exemplary weighting factors for a prediction sample at (1,0) in DC mode in accordance with an embodiment;

FIG. 10 shows a flow chart outlining an exemplary process according toan embodiment of the disclosure; and

FIG. 11 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Video Encoder and Decoder

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick, and the like.

A streaming system may include a capture subsystem (313) that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle play outtiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values that canbe input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation that the intra prediction unit (452) has generated to theoutput sample information as provided by the scaler/inverse transformunit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. En such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector allowed reference area,and so forth. The controller (550) can be configured to have othersuitable functions that pertain to the video encoder (503) optimized fora certain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415) andthe parser (420) may not be fully implemented in the local decoder(533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of 13 pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quad-tree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an ultra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information,

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract dc-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (603), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

Intra Prediction in VVC

FIG. 8A shows an illustration of exemplary intra prediction directionsand corresponding intra prediction modes in some examples (e.g., VVC).In FIG. 8A, there are a total of 95 intra prediction modes (modes−14˜80), among which mode 0 is planar mode (referred to asINTRA_PLANAR), mode 1 is DC mode (referred to as INTRA_DC), and othermodes (modes −14˜−1 and modes 2˜80) are angular (or directional) modes(also referred to as INTRA_ANGULAR). Among the angular (or directional)modes, mode 18 (referred to as INTRA_ANGULAR18) is a horizontal mode,mode 50 (referred to as INTRA_ANGULAR50) is a vertical mode, and mode 2(referred to as INTRA_ANGULAR2) is a diagonal mode that points to abottom-left direction, mode 34 (referred to as INTRA_ANGULAR34) is adiagonal mode that points to a top-left direction, and mode 66 (referredto as INTRA_ANGULAR66) is a diagonal mode that points to a top-rightdirection, Modes −14˜−1 and Modes 67˜80 are referred to as wide-angleintra prediction (WAIP) modes. Example angular intra prediction modesand their corresponding intra prediction angles are tabulated in FIG.8B.

Position Dependent Prediction Combination (PDPC) Filtering Process

According to aspects of the disclosure, position dependent predictioncombination (PDPC) may be applied to the following intra modes withoutsignaling: planar, DC, WAIP modes, horizontal, vertical, bottom-leftangular mode (mode 2) and its 8 adjacent angular modes (modes 3˜10), andtop-right angular mode (mode 66) and its 8 adjacent angular modes (modes58˜65).

In an embodiment, a prediction sample pred′[x][y] located at a position(x, y) in a current block is predicted using an intra prediction mode(e.g., DC, planar, or an angular mode) and a linear combination ofreference samples according to Eq. 1.pred′[x][y]=(wL×R(−1,y)+wT×R(x,−1)−wTL×R(−1,−1)+(64−wL−wT+wTL)×pred[x][y]+32)>>6  (Eq.1)where pred[x][y] is an intra prediction value resulted from the intraprediction mode, R(x, −1) represents a (unfiltered) reference samplethat is located at a top reference line of the current sample (x, y) andhas the same horizontal coordinate as the current sample (x, y), R(−1,y) represents a (unfiltered) reference sample that is located at a leftreference line of the current sample (x, y) and has the same verticalcoordinate as the current sample (x, y), R(−1, −1) represents areference sample located at a top-left corner of the current block, andwT, wL, and wTL denote weighting factors.

In an embodiment, when the intra prediction mode is DC mode, the weightfactors may be calculated by Eq. 2-Eq. 5.wT=32>>((y<<1)>>nScale)  (Eq. 2)wL=32>>((x<<1)>>nScale)  (Eq. 3)wTL=+(wL>>4)+(wT>>4)  (Eq. 4)nScale=(log 2(width)+log 2(height)−2)>>2  (Eq. 5)where wT denotes the weighting factor for the reference sample (x, −1),wL denotes the weighting factor for the reference sample (−1, y), andwTL denotes the weighting factor for the top-left reference sample (−1,−1), nScale (referred to as weighting factor decrement rate) specifieshow fast these weighting factors decrease along an axis (e.g., wLdecreases from left to right along the x-axis, or wT decreases from topto bottom along the y-axis). The constant 32 in Eq. 2 and Eq. 3 denotesan initial weighting factor of a neighboring sample (e.g., a topneighboring sample, a left neighboring sample, or a top-left neighboringsample). The initial weighting factor is also assigned to a top-leftsample of the current block. The weighting factors of neighboringsamples in the PDPC filtering process are equal to or less than theinitial weighting factor.

In an embodiment, when the intra prediction mode is planar mode, wTL isset equal to 0; when the intra prediction mode is horizontal mode, wTLis set equal to wT; and when the intra prediction mode is vertical mode,wTL is set equal to wL. The PDPC weighting factors can be calculatedwith add operations and shift operations. The value of pred′[x][y] canbe computed in a single step using Eq. 1.

FIG. 9A shows exemplary weighting factors for a prediction sample at (0,0) in DC mode. In the FIG. 9A example, the current block is a 4×4 block(width=height=4), thus nScale is 0. Then, wT is 32, wL is 32, and wTL is4.

FIG. 9B shows exemplary weighting factors for a prediction sample at (1,0) in DC mode. In the FIG. 9B example, the current block is a 4×4 block(width=height=4), thus nScale is 0. Then, wT is 32, wL is 8, and wTL is2.

In some embodiments, when the PDPC filtering process is applied to DC,planar, horizontal, and vertical intra modes, additional boundaryfilters are not needed, such as the HEVC DC mode boundary filter orhorizontal/vertical mode edge filters.

Exemplary PDPC Filtering Process

In some examples, inputs of the PDPC filtering process include:

-   -   the intra prediction mode that is represented by preModeIntra;    -   the width of the current block that is represented nTbW;    -   the height of the current block that is represented by nTbH;    -   the width of the reference samples that is represented by refW;    -   the height of the reference samples that is represented by refH;    -   the predicted samples that are represented by predSamples[x][y],        with x=0 . . . nTbW−1 and y=0 . . . nTbH−1;    -   the unfiltered reference (also referred to as neighboring)        samples that are represented by p[x][y], with x=−1, y=−1 . . .        refH−1 and x=0 . . . refW−1, y=−1; and    -   the color component of the current block that is represented by        cIdx.

Depending on the value of cIdx, the function clip1Cmp is set as follows:

-   -   If cIdx is equal to 0, clip1Cmp is set equal to Clip1_(γ).    -   Otherwise, clip1Cmp is set equal to Clip1_(C).

Further, outputs of the PDPC filtering process are the modifiedpredicted samples predSamples′[x][y] with x=0 . . . nTbW−1 and y=0 . . .nTbH−1.

Then, a scaling factor nScale may be calculated by Eq. 6.nScale=((Log 2(nTbW)+Log 2(nTbH)−2)>>2)  (Eq. 6)

Further, a reference sample array mainRef[x] with x=0 . . . refW may bedefined as the array of unfiltered reference samples above the currentblock and another reference sample array sideRef[y] with y=0 . . . refHmay be defined as the array of unfiltered reference samples to the leftof the current block. The reference sample arrays mainRef[x] andsideRef[y] may be derived from unfiltered reference samples according toEq. 7-Eq. 8, respectively.mainRef[x]=p[x][−1]  (Eq. 7)sideRef[y]=p[−1][y]  (Eq. 8)

For each location (x, y) in the current block, the PDPC calculation mayuse a reference sample at the top that is denoted as refT[x][y], areference sample at the left that is denoted as refL[x][y], and areference sample at the corner p[−1, −1]. The modified predicted samplemay be calculated by Eq. 9, and the result is suitably clipped accordingto the variable cIdx that is indicative of the color component.predSamples′[x][y]=(wL×refL(x,y)+wT×refT(x,y)−wTL×p(−1,−1)+(64−wL−wT+wTL)×predSamples[x][y]+32)>>6  (Eq.9)

The reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL can be determined based on the intra prediction modepreModeIntra.

When the intra prediction mode preModeIntra is equal to INTRA_PLANAR(e.g., 0, planar mode, or mode 0) or INTRA_DC (e.g., 1, DC mode, or mode1), reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL may be determined according to Eq. 10-Eq. 14.refL[x][y]=p[−1][y]  (Eq. 10)refT[x][y]=p[x][−1]  (Eq. 11)wT[y]=32>>((y<<1)>>nScale)  (Eq. 12)wL[x]=32>>((x<<1)>>nScale)  (Eq. 13)wTL[x][y]=(predModeIntra==INTRA_DC)?((wL[x]>>4)+(wT[y]>>4)):0  (Eq. 14)

Otherwise, when the intra prediction mode preModeIntra is equal toINTRA_ANGULAR18 (e.g., 18, horizontal mode, or mode 18) orINTRA_ANGULAR50 (e.g., 50, vertical mode, or mode 50), reference samplesrefT[x][y], refL[x][y], and the weighting factors wL, wT, and wTL may bedetermined according to Eq. 15-Eq. 19.refL[x][y]=p[−1][y]  (Eq. 15)refT[x][y]=p[x][−1]  (Eq. 16)wT[y]=(predModeIntra==INTRA_ANGULAR18)?32>>((y<<1)>>nScale): 0   (Eq.17)wL[x]=(predModeIntra==INTRA_ANGULAR50)?32>>((x<<1)>>nScale):0   (Eq. 18)wTL[x][y]=(predModeIntra==INTRA_ANGULAR18)?wT[y]:wL[x]  (Eq. 19)

Otherwise, when the intra prediction mode preModeIntra is equal toINTRA_ANGULAR2 (e.g., 2, or mode 2) or INTRA_ANGULAR66 (e.g., 66, ormode 66), reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 20-Eq. 24.refL[x][y]=p[−1][x+y+1]  (Eq. 20)refT[x][y]=p[x+y+1][−1]  (Eq. 21)wT[y]=(32>>1)>>((y<<1)>>nScale)  (Eq. 22)wL[x]=(32>>1)>>((x<<1)>>nScale)  (Eq. 23)wTL[x][y]=0  (Eq. 24)

Otherwise, when the intra prediction mode preModeIntra is less than orequal to INTRA_ANGULAR10 (e.g., 10, or mode 10), for each location (x,y), variables dXPos[y], dXFrac[y], dXInt[y], and dX[x][y] may be derivedbased on a variable invAngle that is a function of the intra predictionmode preModeIntra. The invAngle can be determined based on a look-uptable that stores a corresponding invAngle value to each intraprediction mode, and then the reference samples refT[x][y], refL[x][y],and the weighting factors wL, wT, and wTL can be determined based on thevariables dXPos[y], dXFrac[y], dXInt[y], and dX[x][y].

The variables dXPos[y], dXFrac[y], dXInt[y], and dX [x][y] may bedetermined according to Eq. 25-Eq. 28.dXPos[y]=((y+1)×invAngle+2)>>2  (Eq. 25)dXFrac[y]=dXPos[y]&63  (Eq. 26)dX Int[y]=dXPos[y]>>6  (Eq. 27)dX[x][y]=x+dX Int[y]  (Eq. 28)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 29-Eq. 33.refL[x][y]=0  (Eq. 29)refT[x][y]=(dX[x][y]<refW−1)?mainRef[dX[x][y]+(dXFrac[y]>>5)]: 0  (Eq.30)wT[y]=(dX[y]<refW−1)?32>>((y<<1)>>nScale): 0  (Eq. 31)wL[x]=0  (Eq. 32)wTL[x][y]=0  (Eq. 33)

Otherwise, when the intra prediction mode preModeIntra is greater thanor equal to INTRA_ANGULAR58 (e.g., 58, or mode 58), variables dYPos[x],dYFrac[x], dYInt[x], and dY[x][y] may be derived based on a variableinvAngle that is a function of the intra prediction mode preModeIntra.The invAngle can be determined based on a look-up table that stores acorresponding invAngle value for each intra prediction mode, and thenthe reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL may be determined based on the variables dYPos[x],dYFrac[x], dYInt[x], and dY[x][y].

The variables dYPos[x], dYFrac[x], dYInt[x], and dY[x][y] may bedetermined according to Eq. 34-Eq. 37.dYPos[x]=((x+1)×invAngle+2)>>2  (Eq. 34)dYFrac[x]=dYPos[x]&63  (Eq. 35)dY Int[x]=dYPos[x]>>6  (Eq. 36)dY[x][y]=x+dY Int[x]  (Eq. 37)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 38-Eq. 42.refL[x][y]=(dY[x][y]<refH−1)?sideRef[dY[x][y]+(dYFrac[x]>>5)]: 0  (Eq.38)refT[x][y]=0  (Eq. 39)wT[y]=0  (Eq. 40)wL[x]=(dY[x]<refH−1)?32>>((x<<1)>>nScale): 0  (Eq. 41)wTL[x][y]=0  (Eq. 42)

Otherwise, when the variable preModeIntra is between modes 11-57 and isnot one of mode 18 and mode 50, then the reference samples refT[x][y],refL[x][y], and the weighting factors wL, wT, and wTL are all set equalto 0.

Finally, the values of the filtered samples filtSamples[x][y], with x=0. . . nTbW−1, y=0 . . . nTbH−1 may be derived according to Eq. 43.filtSamples[x][y]=clip1Cmp((refL[x][y]×wL+refT[x][y]×wT−p[−1][−1]×wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])×predSamples[x][y]+32)>>6)  (Eq. 43)

In some examples (e.g., in VVC), for a nTbW×nTbH transform block in anCbW×nCbH current block, when performing the intra prediction with PDPC,if the current block is not coded in intra sub-partitions (ISP) mode(i.e., IntraSubPartitionsSplitType is equal to ISP_NO_SPLIT, asindicated in VVC Draft v5), the range of top available reference samples(refW) is set as 2×nTbW, and the range of left available referencesamples (refH) is set as 2×nTbH. Otherwise, if ISP is applied for thecurrent block (i.e., IntraSubPartitionsSplitType is not equal toISP_NO_SPLIT, as indicated in VVC Draft v5), the range of top availablereference samples (refW) is set as 2×nCbW, and the range of leftavailable reference samples (refH) is set as 2×nCbH.

Improvement Techniques for PDPC

In the above section “Exemplary PDPC filtering process” or some relatedexamples (such as in VTM5.0), different PDPC processes may be applied tothe infra coded blocks with a diagonal intra prediction mode and modesadjacent to the diagonal intra prediction mode. For example, differentPDPC processes may be applied to mode 2 and its adjacent modes (e.g.,mode indices being equal to or less than 10). In another example,different PDPC processes are applied to mode 66 and its adjacent modes(e.g., mode indices being equal to or greater than 58). However, theprediction process of the diagonal prediction modes and their adjacentmodes are similar, and there is no clear benefit to keep different PDPCprocess for these modes. Accordingly, aspects of the disclosure provideimprovement techniques for PDPC process.

The present techniques or methods may be used separately or combined inany order. Note that, in the following sections, PDPC may be used as ageneral term for position dependent boundary filtering process forprediction samples which applies a linear combination of the predictionsamples and the neighboring reconstructed samples usingposition-dependent weightings, and the results may be used to replacethe original prediction samples. Accordingly, the PDPC process is notlimited to the process described in the above section “Exemplary PDPCfiltering process”.

In addition, in the following descriptions, the diagonal intraprediction modes may be mode 2 and mode 66 in FIG. 8A, the modesadjacent to the mode 2 may have mode indices that are less than thehorizontal mode (e.g., intra mode index is less than 18), and the modesadjacent to the mode 66 may have mode indices that are greater than thevertical mode (e.g., intra mode index is greater than 50).

According to aspects of the disclosure, the same PDPC process (e.g.,same range of available reference samples, same weighting factorsapplied for each position) is applied to the diagonal intra predictionmodes and the modes adjacent to the diagonal ultra prediction modes.

In one embodiment, the diagonal intra prediction modes may be mode 2 andmode 66 in FIG. 8A, and the modes adjacent to the diagonal ultraprediction modes may be modes −1˜−14, modes 3˜10, modes 58˜65, and modes67˜80 in FIG. 8A.

In one embodiment, only a subset of available neighboring referencesamples can be used by PDPC process for blocks using diagonal predictionmodes, but all the available neighboring reference samples can be usedby PDPC process for blocks with modes adjacent to the diagonalprediction modes. For example, only refW−K above neighboring referencesamples and refH−K left neighboring reference samples are used in PDPCprocess for blocks predicted using diagonal intra prediction modes(e.g., mode 2 and mode 66 in VVC Draft v5), where refW and refHrespectively denote the total number of available top and left referencesamples (as specified in VVC Draft v5 clause “General intra sampleprediction” and also described in the above section “Exemplary PDPCfiltering process”), and K is a positive integer (e.g., 1, 2, 3, or 4).

In one embodiment, for the diagonal mode (e.g., mode 2 and mode 66 inVVC Draft v5), all the top and left available reference samples can beused for PDPC except the right most sample and bottom most sample.

Exemplary Modifications of PDPC Process

In some embodiments (e.g., following embodiments A˜E), the PDPC processcan be modified as follows.

Embodiment A

Example inputs of the PDPC filtering process include:

-   -   the intra prediction mode that is represented by preModeIntra;    -   the width of the current block that is represented nTbW;    -   the height of the current block that is represented by nTbH;    -   the width of the reference samples that is represented by refW;    -   the height of the reference samples that is represented by refH;    -   the predicted samples that are represented by predSamples        [x][y], with x=0 . . . nTbW−1 and y=0 . . . nTbH−1;    -   the unfiltered reference (also referred to as neighboring)        samples that are represented by p[x][y], with x=−1, y=−1 . . .        refH−1 and x=0 . . . refW−1, y=−1; and    -   the color component of the current block that is represented by        cIdx.

Depending on the value of cIdx, the function clip1Cmp may be set asfollows:

-   -   If cIdx is equal to 0, clip1Cmp is set equal to Clip1_(γ).    -   Otherwise, clip1Cmp is set equal to Clip1_(C).

Further, outputs of the PDPC filtering process may be the modifiedpredicted samples predSamples′[x][y] with x=0 . . . nTbW−1 and y=0 . . .nTbH−1.

Then, a scaling factor nScale may be calculated by Eq. 44.nScale=((Log 2(nTbW)+Log 2(nTbH)−2)>>2)  (Eq. 44)

Further, a reference sample array mainRef[x] with x=0 . . . refW may bedefined as the array of unfiltered reference samples above the currentblock and another reference sample array sideRef[y] with y=0 . . . refHmay be defined as the array of unfiltered reference samples to the leftof the current block. The reference sample arrays mainRef[x] andsideRef[y] A may be derived from unfiltered reference samples accordingto Eq. 45-Eq. 46, respectively.mainRef[x]=p[x][−1]  (Eq. 45)sideRef[y]=p[−1][y]  (Eq. 46)

For each location (x, y) in the current block, the PDPC calculation mayuse a reference sample at the top that is denoted as refT[x][y], areference sample at the left that is denoted as refL[x][y], and areference sample at the corner p[−1, −1]. In some examples, the modifiedpredicted sample may be calculated by Eq. 47, and the result is suitablyclipped according to the variable cIdx that is indicative of the colorcomponent.predSamples′[x][y]=(wL×refL(x,y)+wT×refT(x,y)−wTL×p(−1,−1)+(64−wL−wT+wTL)×predSamples[x][y]+32)>>6  (Eq.47)

The reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL can be determined based on the intra prediction modepreModeIntra.

When the intra prediction mode preModeIntra is equal to INTRA_PLANAR(e.g., 0, planar mode, or mode 0) or INTRA_DC (e.g., 1, DC mode, or mode1), reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL may be determined according to Eq. 48-Eq. 52.refL[x][y]=p[−1][y]  (Eq. 48)refT[x][y]=p[x][−1]  (Eq. 49)wT[y]=32>>((y<<1)>>nScale)  (Eq. 50)wL[x]=32>>((x<<1)>>nScale)  (Eq. 51)wTL[x][y]=(predModeIntra==INTRA_DC)?((wL[x]>>4)+(wT[y]>>4)): 0  (Eq. 52)

Otherwise, when the intra prediction mode preModeIntra is equal toINTRA_ANGULAR18 (e.g., 18, horizontal mode, or mode 18) orINTRA_ANGULAR50 (e.g., 50, vertical mode, or mode 50), reference samplesrefT[x][y], refL[x][y], and the weighting factors wL, wT, and wTL may bedetermined according to Eq. 53-Eq. 57.refL[x][y]=p[−1][y]  (Eq. 53)refT[x][y]=p[x][−1]  (Eq. 54)wT[y]=(predModeIntra==INTRA_ANGULAR18)?32>>((y<<1)>>nScale):0   (Eq. 55)wL[x]=(predModeIntra==INTRA_ANGULAR50)?32>>((x<<1)>>nScale): 0   (Eq.56)wTL[x][y]=(predModeIntra==INTRA_ANGULAR18)?wT[y]:wL[x]  (Eq. 57)

Otherwise, when the intra prediction mode preModeIntra is less than orequal to INTRA_ANGULAR10 (e.g., 10, or mode 10), for each location (x,y), variables dXPos[y], dXFrac[y], dXInt[y], and dX[x][y] may be derivedbased on a variable invAngle that is a function of the intra predictionmode preModeIntra. The invAngle can be determined based on a look-uptable that stores a corresponding invAngle value to each intraprediction mode, and then the reference samples refT[x][y], refL[x][y],and the weighting factors wL, wT, and wTL may be determined based on thevariables dXPos[y], dXFrac[y], dXInt[y], and dX[x][y].

For example, the variables dXPos[y], dXFrac[y], dXInt[y], and dX[x][y]may be determined according to Eq. 58-Eq. 61.dXPos[y]=((y+1)×invAngle+2)>>2  (Eq. 58)dXFrac[y]=dXPos[y]&63  (Eq. 59)dX Int[y]=dXPos[y]>>6  (Eq. 60)dX[x][y]=x+dX Int[y]  (Eq. 61)

Then, the reference samples refT[x][y], refL [x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 62-Eq. 66.refL[x][y]=0  (Eq. 62)refT[x][y]=(dX[x][y]<refW−1)?mainRef[dX[x][y]+(dXFrac[y]>>5)]: 0  (Eq.63)wT[y]=(dX[y]<refW−1)?32>>((y<<1)>>nScale): 0  (Eq. 64)wL[x]=0  (Eq. 65)wTL[x][y]=0  (Eq. 66)

Otherwise, when the intra prediction mode preModeIntra is greater thanor equal to INTRA_ANGULAR58 (e.g., 58, or mode 58), variables dYPos[x],dYFrac[x], dYInt[x], and dY[x][y] may be derived based on a variableinvAngle that is a function of the intra prediction mode preModeIntra.The invAngle can be determined based on a look-up table that stores acorresponding invAngle value for each intra prediction mode, and thenthe reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL may be determined based on the variables dYPos[x],dYFrac[x], dYInt[x], and dY[x][y].

For example, the variables dYPos[x], dYFrac[x], dYInt[x], and dY[x][y]may be determined according to Eq. 67-Eq. 70.dYPos[x]=((x+1)×invAngle+2)>>2  (Eq. 67)dYFrac[x]=dYPos[x]&63  (Eq. 68)dY Int[x]=dYPos[x]>>6  (Eq. 69)dY[x][y]=x+dY Int[x]  (Eq. 70)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 71-Eq. 75.refL[x][y]=(dY[x][y]<refH−1)?sideRef[dY[x][y]+(dYFrac[x]>>5)]: 0  (Eq.71)refT[x][y]=0  (Eq. 72)wT[y]=0  (Eq. 73)wL[x]=(dY[x]<refH−1)?32>>((x<<1)>>nScale):0  (Eq. 74)wTL[x][y]=0  (Eq. 75)

Otherwise, when the variable preModeIntra is between modes 11-57 and isnot one of mode 18 and mode 50, then the reference samples refT[x][y,refL[x][y], and the weighting factors wL, wT, and wTL are all set equalto 0.

Finally, the values of the filtered samples filtSamples[x][y], with x=0. . . nTbW−1, y=0 . . . nTbH−1 may be derived according to Eq. 76.filtSamples[x][y]=clip1Cmp((refL[x][y]×wL+refT[x][y]×wT−p[−1][−1]×wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])×predSamples[x][y]+32)>>6)  (Eq. 76)

The difference between. Embodiment A and the above section “ExemplaryPDPC filtering process” is that in Embodiment A, the same PDPC processis applied to a diagonal intra prediction mode and modes adjacent to thediagonal intra prediction mode. In an example, the same PDPC process isapplied to mode 2 and modes adjacent to the mode 2 (e.g., mode indicesbeing equal to or less than 10). In another example, the same PDPCprocess is applied to mode 66 and modes adjacent to mode 66 (e.g., modeindices being equal to or greater than 58).

Embodiment B

Example inputs of the PDPC filtering process include:

-   -   the intra prediction mode that is represented by preModeIntra;    -   the width of the current block that is represented nTbW;    -   the height of the current block that is represented by nTbH;    -   the width of the reference samples that is represented by refW;    -   the height of the reference samples that is represented by refH;    -   the predicted samples that are represented by predSamples[x][y],        with x=0 . . . nTbW−1 and y=0 . . . nTbH−1;    -   the unfiltered reference (also referred to as neighboring)        samples that are represented by p[x][y], with x=−1, y=−1 . . .        refH−1 and x=0 . . . refW−1, y=−1; and    -   the color component of the current block that is represented by        cIdx.

Depending on the value of cIdx, the function clip1Cmp is set as follows:

-   -   If cIdx is equal to 0, clip1Cmp is set equal to Clip1_(γ).    -   Otherwise, clip1Cmp is set equal to Clip1_(C).

Further, outputs of the PDPC filtering process are the modifiedpredicted samples predSamples′[x][y] with x=0 . . . nTbW−1 and y=0 . . .nTbH−1.

Then, a scaling factor nScale may be calculated by Eq. 77.nScale=((Log 2(nTbW)+Log 2(nTbH)−2)>>2)  (Eq. 77)

Further, a reference sample array mainRef[x] with x=0 . . . refW may bedefined as the array of unfiltered reference samples above the currentblock and another reference sample array sideRef[y] with y=0 . . . refHmay be defined as the array of unfiltered reference samples to the leftof the current block. The reference sample arrays mainRef[x] andsideRef[y] may be derived from unfiltered reference samples according toEq. 78-Eq. 79, respectively.mainRef[x]=p[x][−1]  (Eq. 78)sideRef[y]=p[−1][y]  (Eq. 79)

For each location (x, y) in the current block, the PDPC calculation mayuse a reference sample at the top that is denoted as refT[x][y], areference sample at the left that is denoted as refL[x][y], and areference sample at the corner p[−1, −1]. In some examples, the modifiedpredicted sample may be calculated by Eq. 80, and the result is suitablyclipped according to the variable cIdx that is indicative of the colorcomponent.predSamples′[x][y]=(wL×refL(x,y)+wT×refT(x,y)−wTL×p(−1,−1)+(64−wL−wT+wTL)×predSamples[x][y]+32)>>6  (Eq.80)

The reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL can be determined based on the intra prediction modepreModeIntra.

When the intra prediction mode preModeIntra is equal to INTRA_PLANAR(e.g., 0, planar mode, or mode 0) or INTRA_DC (e.g., 1, DC mode, or mode1), reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL may be determined according to Eq. 81-Eq. 85.refL[x][y]=p[−1][y]  (Eq. 81)refT[x][y]=p[x][−1]  (Eq. 82)wT[y]=32>>((y<<1)>>nScale)  (Eq. 83)wL[x]=32>>((x<<1)>>nScale)  (Eq. 84)wTL[x][y]=(predModeIntra==INTRA_DC)?((wL[x]>>4)+(wT[y]>>4)): 0  (Eq. 85)

Otherwise, when the intra prediction mode preModeIntra is equal toINTRA_ANGULAR18 (e.g., 18, horizontal mode, or mode 18) orINTRA_ANGULAR50 (e.g., 50, vertical mode, or mode 50), reference samplesrefT[x][y], refL[x][y], and the weighting factors wL, wT, and wTL may bedetermined according to Eq. 86-Eq. 90.refL[x][y]=p[−1][y]  (Eq. 86)refT[x][y]=p[x][−1]  (Eq. 87)wT[y]=(predModeIntra==INTRA_ANGULAR18)?32>>((y<<1)>>nScale): 0   (Eq.88)wL[x]=(predModeIntra==INTRA_ANGULAR50)?32>>((x<<1)>>nScale): 0   (Eq.89)wTL[x][y]=(predModeIntra==INTRA_ANGULAR18)?wT[y]:wL[x]  (Eq. 90)

Otherwise, when the intra prediction mode preModeIntra is less than orequal to INTRA_ANGULAR10 (e.g., 10, or mode 10), for each location (x,y), variables dXPos[y], dXInt[y], and dX[x][y] may be derived based on avariable invAngle that is a function of the intra prediction modepreModeIntra. The invAngle can be determined based on a look-up tablethat stores a corresponding invAngle value to each intra predictionmode, and then the reference samples refT[x][y], refL[x][y], and theweighting factors wL, wT, and wTL may be determined based on thevariables dXPos[y], dXInt[y], and dX[x][y].

For example, the variables dXPos[y], dXInt[y], and dX[x][y] may bedetermined according to Eq. 91-Eq. 93.dXPos[y]=((y+1)×invAngle+2)>>2  (Eq. 91)dX Int[y]=(dXPos[y]+32)>>6  (Eq. 92)dX[x][y]=x+dX Int[y]  (Eq. 93)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 94-Eq. 98.refL[x][y]=0  (Eq. 94)refT[x][y]=(dX[x][y]<refW)?mainRef[dX[x][y]]: 0  (Eq. 95)T[y]=(dX[y]<refW)?32>>((y<<1)>>nScale): 0  (Eq. 96)wL[x]=0  (Eq. 97)wTL[x][y]=0  (Eq. 98)

Otherwise, when the intra prediction mode preModeIntra is greater thanor equal to INTRA_ANGULAR58 (e.g., 58, or mode 58), variables dYPos[x],dYInt[x], and dY[x][y] may be derived based on a variable invAngle thatis a function of the intra prediction mode preModeIntra. The invAnglecan be determined based on a look-up table that stores a correspondinginvAngle value for each intra prediction mode, and then the referencesamples refT[x][y], refL[x][y], and the weighting factors wL, wT, andwTL may be determined based on the variables dYPos[x], dYInt[x], anddY[x][y].

For example, the variables dYPos[x], dYInt[x], and dY[x][y] may bedetermined according to Eq. 99-Eq. 101.dYPos[x]=((x+1)×invAngle+2)>>2  (Eq. 99)dY Int[x]=(dYPos[x]+32)>>6  (Eq. 100)dY[x][y]=x+dY Int[x]  (Eq. 101)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 102-Eq. 106.refL[x][y]=(dY[x][y]<refH)?sideRef[dY[x][y]]: 0  (Eq. 102)refT[x][y]=0  (Eq. 103)wT[y]=0  (Eq. 104)wL[x]=(dY[x]<refH)?32>>((x<<1)>>nScale):0  (Eq. 105)wTL[x][y]=0  (Eq. 106)

Otherwise, when the variable preModeIntra is between modes 11-57 and isnot one of mode 18 and mode 50, then the reference samples refT[x][y,refL[x][y], and the weighting factors wL, wT, and wTL are all set equalto 0.

Finally, the values of the filtered samples filtSamples[x][y], with x=0. . . nTbW−1, y=0 . . . nTbH−1 may be derived according to Eq. 107:filtSamples[x][y]=clip1Cmp((refL[x][y]×wL+refT[x][y]×wT−p[−1][−1]×wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])×predSamples[x][y]+32)>>6)  (Eq. 107)

The difference between Embodiment A and Embodiment B is that inEmbodiment B, when the intra prediction mode preModeIntra is less thanor equal to INTRA_ANGULAR10, dXFrac[y] (Eq. 59) is not calculated anddXInt[y] may be calculated in a different way (i.e., Eq. 60 vs. Eq. 92),so that refT[x][y] and wT[y] are calculated in different ways fromEmbodiment A (i.e., Eq. 63 vs. Eq. 95, and Eq. 64 vs. Eq. 96).Similarly, when the intra prediction mode preModeIntra is greater thanor equal to INTRA_ANGULAR58, in Embodiment B, dYFrac[x] (Eq. 68) is notcalculated and dYInt[x] may be calculated in a different way (Eq. 69 vs.Eq. 100), so that refL[x][y] and wL[y] are calculated in different waysfrom Embodiment A (i.e., Eq. 71 vs. Eq. 102, and Eq. 74 vs. Eq. 105).

Embodiment C

Example inputs of the PDPC filtering process include:

-   -   the intra prediction mode that is represented by preModeIntra;    -   the width of the current block that is represented nTbW;    -   the height of the current block that is represented by nTbH;    -   the width of the reference samples that is represented by refW;    -   the height of the reference samples that is represented by refH;    -   the predicted samples that are represented by predSamples        [x][y], with x=0 . . . nTbW−1 and y=0 . . . nTbH−1;    -   the unfiltered reference (also referred to as neighboring)        samples that are represented by p[x][y], with x=−1, y=−1 . . .        refH−1 and x=0 . . . refW−1, y=−1; and    -   the color component of the current block that is represented by        cIdx.

Depending on the value of cIdx, the function clip1Cmp is set as follows:

-   -   If cIdx is equal to 0, clip1Cmp is set equal to Clip1_(γ).    -   Otherwise, clip1Cmp is set equal to Clip1_(C).

Further, outputs of the PDPC filtering process are the modifiedpredicted samples predSamples′[x][y] with x=0 . . . nTbW−1 and y=0 . . .nTbH−1.

Then, a scaling factor nScale may be calculated by Eq. 108.nScale=((Log 2(nTbW)+Log 2(nTbH)−2)>>2)  (Eq. 108)

Further, a reference sample array mainRef[x] with x=0 . . . refW may bedefined as the array of unfiltered reference samples above the currentblock and another reference sample array sideRef[y] with y=0 . . . refHmay be defined as the array of unfiltered reference samples to the leftof the current block. The reference sample arrays mainRef[x] andsideRef[y] may be derived from unfiltered reference samples according toEq. 109-Eq. 110, respectively.mainRef[x]=p[x][−1]  (Eq. 109)sideRef[y]=p[−1][y]  (Eq. 110)

For each location (x, y) in the current block, the PDPC calculation mayuse a reference sample at the top that is denoted as refT[x][y], areference sample at the left that is denoted as refL[x][y], and areference sample at the corner p[−1, −1]. In some examples, the modifiedpredicted sample may be calculated by Eq. 111, and the result issuitably clipped according to the variable cIdx that is indicative ofthe color component.predSamples′[x][y]=(wL×refL(x,y)+wT×refT(x,y)−wTL×p(−1,−1)+(64−wL−wT+wTL)×predSamples[x][y]+32)>>6  (Eq.111)

The reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL can be determined based on the intra prediction modepreModeIntra.

When the intra prediction mode preModeIntra is equal to INTRA_PLANAR(e.g., 0, planar mode, or mode 0) or INTRA_DC (e.g., 1, DC mode, or mode1), reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL may be determined according to Eq. 112-Eq. 116.refL[x][y]=p[−1][y]  (Eq. 112)refT[x][y]=p[x][−1]  (Eq. 113)wT[y]=32>>((y<<1)>>nScale)  (Eq. 114)wL[x]=32>>((x<<1)>>nScale)  (Eq. 115)wTL[x][y]=(predModeIntra==INTRA_DC)?((wL[x]>>4)+(wT[y]>>4)): 0  (Eq.116)

Otherwise, when the intra prediction mode preModeIntra is equal toINTRA_ANGULAR18 (e.g., 18, horizontal mode, or mode 18) orINTRA_ANGULAR50 (e.g., 50, vertical mode, or mode 50), reference samplesrefT[x][y], refL[x][y], and the weighting factors wL, wT, and wTL may bedetermined according to Eq. 117-Eq. 121.refL[x][y]=p[−1][y]  (Eq. 117)refT[x][y]=p[x][−1]  (Eq. 118)wT[y]=(predModeIntra==INTRA_ANGULAR18)?32>>((y<<1)>>nScale): 0   (Eq.119)wL[x]=(predModeIntra==INTRA_ANGULAR50)?32>>((x<<1)>>nScale):0   (Eq.120)wTL[x][y]=(predModeIntra==INTRA_ANGULAR18)?wT[y]: wL[x]  (Eq. 121)

Otherwise, when the intra prediction mode pre Mode Intra is less than orequal to INTRA_ANGULAR1.0 (e.g., 10, or mode 10), for each location (x,y), variables dXInt[y] and dX [x][y] may be derived based on a variableinvAngle that is a function of the intra prediction mode preModeIntra.The invAngle can be determined based on a look-up table that stores acorresponding invAngle value to each intra prediction mode, and then thereference samples refT[x][y], refL[x][y], and the weighting factors wL,wT, and wTL may be determined based on the variables dXInt[y] anddX[x][y].

For example, the variables dXInt[y] and dX[x][y] may be determinedaccording to Eq. 122-Eq. 123.dX Int[y]=((y+1)×invAngle+128)>>8  (Eq. 122)dX[x][y]=x+dX Int[y]  (Eq. 123)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 124-Eq. 128.refL[x][y]=0  (Eq. 124)refT[x][y]=(dX[x][y]<refW)?mainRef[dX[x][y]]: 0  (Eq. 125)wT[y]=(dX[y]<refW)?32>>((y<<1)>>nScale): 0  (Eq. 126)wL[x]=0  (Eq. 127)wTL[x][y]=0  (Eq. 128)

Otherwise, when the intra prediction mode preModeIntra is greater thanor equal to INTRA_ANGULAR58 (e.g., 58, or mode 58), variables dYInt[x]and dY[x][y] may be derived based on a variable invAngle that is afunction of the intra prediction mode preModeIntra. The invAngle can bedetermined based on a look-up table that stores a corresponding invAnglevalue for each intra prediction mode, and then the reference samplesrefT[x][y], refL[x][y], and the weighting factors wL, wT, and wTL may bedetermined based on the variables dYInt[x] and dY[x][y].

For example, the variables dYInt[x] and dY[x][y] may be determinedaccording to Eq. 129-Eq. 130.dY Int[x]=((x+1)×invAngle+128)>>8  (Eq. 129)dY[x][y]=x+dY Int[x]  (Eq. 130)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 131-Eq. 135.refL[x][y]=[x][y]<refH)?sideRef[dY[x][y]]: 0  (Eq. 131)refT[x][y]=0  (Eq. 132)wT[y]=0  (Eq. 133)wL[x]=(dY[x]<refH)?32>>((x<<1)>>nScale):0  (Eq. 134)wTL[x][y]=0  (Eq. 135)

Otherwise, when the variable preModeIntra is between modes 11-57 and isnot one of mode 18 and mode 50, then the reference samples refT[x][y,refL[x][y], and the weighting factors wL, wT, and wTL are all set equalto 0.

Finally, the values of the filtered samples filtSamples[x][y], with x=0. . . nTbW−1, y=0 . . . nTbH−1 may be derived according to Eq. 136:filtSamples[x][y]=clip1Cmp((refL[x][y]×wL+refT[x][y]×wT−p[−1][−1]×wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])×predSamples[x][y]+32)>>6)  (Eq. 136)

The difference between Embodiment B and Embodiment C is that inEmbodiment C, when the intra prediction mode preModeIntra is less thanor equal to INTRA_ANGULAR10, dXPos[y] (Eq. 91) is not calculated anddXInt[y] may be calculated in a different way (i.e., Eq. 92 vs. Eq.122). Similarly, when the intra prediction mode preModeIntra is greaterthan or equal to INTRA_ANGULAR58, in Embodiment C, dYPos[x] (Eq. 99) isnot calculated and dYInt[x] may be calculated in a different way (Eq.100 vs. Eq. 129).

Embodiment D

Example inputs of the PDPC filtering process include:

-   -   the intra prediction mode that is represented by preModeIntra;    -   the width of the current block that is represented nTbW;    -   the height of the current block that is represented by nTbH;    -   the width of the reference samples that is represented by refW;    -   the height of the reference samples that is represented by refH;    -   the predicted samples that are represented by predSamples        [x][y], with x=0 . . . nTbW−1 and y=0 . . . nTbH−1;    -   the unfiltered reference (also referred to as neighboring)        samples that are represented by p[x][y], with x=1, y=1 . . .        refH−1 and x=0 . . . refW−1, y=−1; and    -   the color component of the current block that is represented by        cIdx.

Depending on the value of cIdx, the function clip1Cmp is set as follows:

-   -   If cIdx is equal to 0, clip1Cmp is set equal to Clip1_(γ).    -   Otherwise, clip1Cmp is set equal to Clip1_(C).

Further, outputs of the PDPC filtering process are the modifiedpredicted samples predSamples′[x][y] with x=0 . . . nTbW−1 and y=0 . . .nTbH−1.

Then, a scaling factor nScale may be calculated by Eq. 137.nScale=((Log 2(nTbW)+Log 2(nTbH)−2)>>2)  (Eq. 137)

Further, a reference sample array mainRef[x] with x=0 . . . refW may bedefined as the array of unfiltered reference samples above the currentblock and another reference sample array sideRef[y] with y=0 . . . refHmay be defined as the array of unfiltered reference samples to the leftof the current block. The reference sample arrays mainRef[x] andsideRef[y] may be derived from unfiltered reference samples according toEq. 138-Eq. 139, respectively.mainRef[x]=p[x][−1]  (Eq. 138)sideRef[y]=p[−1][y]  (Eq. 139)

For each location (x, y) in the current block, the PDPC calculation mayuse a reference sample at the top that is denoted as refT[x][y], areference sample at the left that is denoted as refL[x][y], and areference sample at the corner p[−1, −1]. The modified predicted samplemay be calculated by Eq. 140, and the result is suitably clippedaccording to the variable cIdx that is indicative of the colorcomponent.predSamples′[x][y]=(wL×refL(x,y)+wT×refT(x,y)−wTL×p(−1,−1)+(64−wL−wT+wTL)×predSamples[x][y]+32)>>6  (Eq.140)

The reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL can be determined based on the intra prediction modepreModeIntra.

When the intra prediction mode preModeIntra is equal to INTRA_PLANAR(e.g., 0, planar mode, or mode 0) or INTRA_DC (e.g., 1, DC mode, or mode1), reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL may be determined according to Eq. 141-Eq. 145.refL[x][y]=p[−1][y]  (Eq. 141)refT[x][y]=p[x][−1]  (Eq. 142)wT[y]=32>>((y<<1)>>nScale)  (Eq. 143)wL[x]=32>>((x<<1)>>nScale)  (Eq. 144)wTL[x][y]=(predModeIntra==INTRA_DC)?((wL[x]>>4)+(wT[y]>>4)): 0  (Eq.145)

Otherwise, when the intra prediction mode preModeIntra is equal toINTRA_ANGULAR18 (e.g., 18, horizontal mode, or mode 18) orINTRA_ANGULAR50 (e.g., 50, vertical mode, or mode 50), reference samplesrefT[x][y], refL[x][y], and the weighting factors wL, wT, and wTL may bedetermined according to Eq. 146-Eq. 150.refL[x][y]=p[−1][y]  (Eq. 146)refT[x][y]=p[x][−1]  (Eq. 147)wT[y]=(predModeIntra==INTRA_ANGULAR18)?32>>((y<<1)>>nScale): 0   (Eq.148)wL[x]=(predModeIntra==INTRA_ANGULAR50)?32>>((x<<1)>>nScale): 0   (Eq.149)wTL[x][y]=(predModeIntra==INTRA_ANGULAR18)?wT[y]:wL[x]  (Eq. 150)

Otherwise, when the intra prediction mode preModeIntra is equal toINTRA_ANGULAR2 (e.g., 2, or mode 2), for each location (x, y), variablesdXPos[y], dXFrac[y], dXInt[y], and dX[x][y] may be derived based on avariable invAngle that is a function of the intra prediction modepreModeIntra. The invAngle can be determined based on a look-up tablethat stores a corresponding invAngle value to each intra predictionmode, and then the reference samples ref T[x][y], refL[x][y], and theweighting factors wL, wT, and wTL can be determined based on thevariables dXPos[y], dXFrac[y], dXInt[y], and dX[x][y].

The variables dXPos[y], dXFrac[y], dXInt[y], and dX[x][y] may bedetermined according to Eq. 151-Eq. 154.dXPos[y]=((y+1)×invAngle+2)>>2  (Eq. 151)dXFrac[y]=dXPos[y]&63  (Eq. 152)dX Int[y]=dXPos[y]>>6  (Eq. 153)dX[x][y]=x+dX Int[y]  (Eq. 154)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 155-Eq. 159.refL[x][y]=0  (Eq. 155)refT[x][y]=(dX[x][y]<refW−1)?mainRef[dX[x][y]+(dXFrac[y]>>5)]: 0  (Eq.156)wT[y]=(dX[y]<refW−1)?32>>((y<<1)>>nScale): 0  (Eq. 157)wL[x]=0  (Eq. 158)wTL[x][y]=0  (Eq. 159)

Otherwise, when the intra prediction mode preModeIntra is less than orequal to INTRA_ANGULAR10 (e.g., 10, or mode 10), for each location (x,y), variables dXPos[y], dXFrac[y], dXInt[y], and dX[x][y] may be derivedbased on a variable invAngle that is a function of the intra predictionmode preModeIntra. The invAngle can be determined based on a look-uptable that stores a corresponding invAngle value to each intraprediction mode, and then the reference samples refT[x][y], refL[x][y],and the weighting factors wL, wT, and wTL can be determined based on thevariables dXPos[y], dXFrac[y], dXInt[y], and dX [x][y].

The variables dXPos[y], dXFrac[y], dXInt[y], and dX[x][y] may bedetermined according to Eq. 160-Eq. 163.dXPos[y]=((y+1)×invAngle+2)>>2  (Eq. 160)dXFrac[y]=dXPos[y]&63  (Eq. 161)dX Int[y]=dXPos[y]>>6  (Eq. 162)dX[x][y]=x+dX Int[y]  (Eq. 163)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 164-Eq. 168.refL[x][y]=0  (Eq. 164)refT[x][y]=(dX[x][y]<refW−1)?mainRef[dX[x][y]+(dXFrac[y]>>5)]: 0  (Eq.165)wT[y]=(dX[y]<refW−1)?32>>((y<<1)>>nScale): 0  (Eq. 166)wL[x]=0  (Eq. 167)wTL[x][y]=0  (Eq. 168)

Otherwise, when the intra prediction mode preModeIntra is equal toINTRA_ANGULAR66 (e.g., 66, or mode 66), variables dYPos[x], dYFrac[x],dYInt[x], and dY[x][y] may be derived based on a variable invAngle thatis a function of the intra prediction mode preModeIntra. The invAnglecan be determined based on a look-up table that stores a correspondinginvAngle value for each intra prediction mode, and then the referencesamples refT[x][y], refL[x][y], and the weighting factors wL, wT, andwTL may be determined based on the variables dYPos[x], dYFrac[x],dYInt[x], and dY[x][y].

The variables dYPos[x], dYFrac[x], dYInt[x], and dY[x][y] may bedetermined according to Eq. 169-Eq. 172.dYPos[x]=((x+1)×invAngle+2)>>2  (Eq. 169)dYFrac[x]=dYPos[x]&63  (Eq. 170)dY Int[x]=dYPos[x]>>6  (Eq. 171)dY[x][y]=x+dY Int[x]  (Eq. 172)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 173-Eq. 177.refL[x][y]=(dY[x][y]<refH−1)?sideRef[dY[x][y]+(dYFrac[x]>>5)]: 0  (Eq.173)refT[x][y]=0  (Eq. 174)wT[y]=0  (Eq. 175)wL[x]=(dY[x]<refH−1)?32>>((x<<1)>>nScale): 0  (Eq. 176)wTL[x][y]=0  (Eq. 177)

Otherwise, when the intra prediction mode preModeIntra is greater thanor equal to INTRA_ANGULAR58 (e.g., 58, or mode 58), variables dYPos[x],dYFrac[x], dYInt[x], and dY[x][y] may be derived based on a variableinvAngle that is a function of the intra prediction mode preModeIntra.The invAngle can be determined based on a look-up table that stores acorresponding invAngle value for each intra prediction mode, and thenthe reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL may be determined based on the variables dYPos[x],dYFrac[x], dYInt[x], and dY[x][y].

The variables dYPos[x], dYFrac[x], dYInt[x], and dY[x][y] may bedetermined according to Eq. 178-Eq. 181.dYPos[x]=((x+1)×invAngle+2)>>2  (Eq. 178)dYFrac[x]=dYPos[x]&63  (Eq. 179)dY Int[x]=dYPos[x]>>6  (Eq. 180)dY[x][y]=x+dY Int[x]  (Eq. 181)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 182-Eq. 186.refL[x][y]=(dY[x][y]<refH−1)?sideRef[dY[x][y]+(dYFrac[x]>>5)]: 0  (Eq.182)refT[x][y]=0  (Eq. 183)wT[y]=0  (Eq. 184)wL[x]=(dY[x]<refH−1)?32>>((x<<1)>>nScale): 0  (Eq. 185)wTL[x][y]=0  (Eq. 186)

Otherwise, when the variable preModeIntra is between modes 11-57 and isnot one of mode 18 and mode 50, then the reference samples refT[x][y],refL[x][y], and the weighting factors wL, wT, and are all set equal to0.

Finally, the values of the filtered samples filtSamples[x][y], with x=0. . . nTbW−1, y=0 . . . nTbH−1 may be derived according to Eq. 187:filtSamples[x][y]=clip1Cmp((refL[x][y]×wL+refT[x][y]×wT−p[−1][−1]×wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])×predSamples[x][y]+32)>>6)  (Eq. 187)

The Embodiment D is similar to Embodiment A but describes a differentmodified PDPC process for mode 2 and mode 66.

Embodiment E

Example inputs of the PDPC filtering process includes:

-   -   the intra prediction mode that is represented by preModeIntra;    -   the width of the current block that is represented nTbW;    -   the height of the current block that is represented by nTbH;    -   the width of the reference samples that is represented by refW;    -   the height of the reference samples that is represented by refH;    -   the predicted samples that are represented by predSamples        [x][y], with x=0 . . . nTbW−1 and y=0 . . . nTbH−1;    -   the unfiltered reference (also referred to as neighboring)        samples that are represented by p[x][y], with x=−1, y=−1 . . .        refH−1 and x=0 . . . refW−1, y=−1; and    -   the color component of the current block that is represented by        cIdx.

Depending on the value of cIdx, the function clip1Cmp is set as follows:

-   -   If cIdx is equal to 0, clip1Cmp is set equal to Clip1_(γ).    -   Otherwise, clip1Cmp is set equal to Clip1_(C).

Further, outputs of the PDPC filtering process are the modifiedpredicted samples predSamples′[x][y] with x=0 . . . nTbW−1 and y=0 . . .nTbH−1.

Then, a scaling factor nScale may be calculated by Eq. 188.nScale=((Log 2(nTbW)+Log 2(nTbH)−2)>>2)  (Eq. 188)

Further, a reference sample array mainRef[x] with x=0 . . . refW may bedefined as the array of unfiltered reference samples above the currentblock and another reference sample array sideRef[y] with y=0 . . . refHmay be defined as the array of unfiltered reference samples to the leftof the current block. The reference sample arrays mainRef[x] andsideRef[y] may be derived from unfiltered reference samples according toEq. 189-Eq. 190, respectively.mainRef[x]=p[x][−1]  (Eq. 189)sideRef[y]=p[−1][y]  (Eq. 190)

For each location (x, y) in the current block, the PDPC calculation mayuse a reference sample at the top that is denoted as refT[x][y], areference sample at the left that is denoted as refL[x][y], and areference sample at the corner p[−1, −1]. In some examples, the modifiedpredicted sample may be calculated by Eq. 191, and the result issuitably clipped according to the variable cIdx that is indicative ofthe color component.predSamples′[x][y]=(wL×refL(x,y)+wT×refT(x,y)−wTL×p(−1,−1)+(64−wL−wT+wTL)×predSamples[x][y]+32)>>6  (Eq.191)

The reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL can be determined based on the intra prediction modepreModeIntra.

When the intra prediction mode preModeIntra is equal to INTRA_PLANAR(e.g., 0, planar mode, or mode 0) or INTRA_DC (e.g., 1, DC mode, or mode1), reference samples refT[x][y], refL[x][y], and the weighting factorswL, wT, and wTL may be determined according to Eq. 192-Eq. 196.refL[x][y]=p[−1][y]  (Eq. 192)refT[x][y]=p[x][−1]  (Eq. 193)wT[y]=32>>((y<<1)>>nScale)  (Eq. 194)wL[x]=32>>((x<<1)>>nScale)  (Eq. 195)wTL[x][y]=(predModeIntra==INTRA_DC)?((wL[x]>>4)+(wT[y]>>4)): 0  (Eq.196)

Otherwise, when the intra prediction mode pre Mode Intra is equal toINTRA_ANGULAR18 (e.g., 18, horizontal mode, or mode 18) orINTRA_ANGULAR50 (e.g., 50, vertical mode, or mode 50), reference samplesrefT[x][y], refL[x][y], and the weighting factors wL, wT, and wTL may bedetermined according to Eq. 197-Eq. 201.refL[x][y]=p[−1][y]  (Eq. 197)refT[x][y]=p[x][−1]  (Eq. 198)wT[y]=(predModeIntra==INTRA_ANGULAR18)?32>>((y<<1)>>nScale): 0   (Eq.199)wL[x]=(predModeIntra==INTRA_ANGULAR50)?32>>((x<<1)>>nScale): 0   (Eq.200)wTL[x][y]=(predModeIntra==INTRA_ANGULAR18)?wT[y]:wL[x]  (Eq. 201)

Otherwise, when the intra prediction mode preModeIntra is less than orequal to INTRA_ANGULAR10 (e.g., 10, or mode 10), for each location (x,y), variables dXInt[y] and dX [x][y] may be derived based on a variableinvAngle that is a function of the intra prediction mode preModeIntra.The invAngle can be determined based on a look-up table that stores acorresponding invAngle value to each intra prediction mode, and then thereference samples refT[x][y], refL[x][y], and the weighting factors wL,wT, and wTL may be determined based on the variables dXInt[y] anddX[x][y].

For example, the variables dXInt[y] and dX [x][y] may be determinedaccording to Eq. 202-Eq. 203.dX Int[y]=((y+1)×invAngle+128)>>8  (Eq. 202)dX[x][y]=x+dX Int[y]  (Eq. 203)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 204-Eq. 208.refL[x][y]=0  (Eq. 204)refT[x][y]=(dX Int[y]<refW−width−1)?mainRef[dX[x][y]]: 0  (Eq. 205)wT=32>>((y<<1)>>nScale)  (Eq. 206)wL[x]=0  (Eq. 207)wTL[x][y]=0  (Eq. 208)

Otherwise, when the intra prediction mode preModeIntra is greater thanor equal to INTRA_ANGULAR58 (e.g., 58, or mode 58), variables dYInt[x]and dY[x][y] may be derived based on a variable invAngle that is afunction of the intra prediction mode preModeIntra. The invAngle can bedetermined based on a look-up table that stores a corresponding invAnglevalue for each intra prediction mode, and then the reference samplesrefT[x][y], refL[x][y], and the weighting factors wL, wT, and wTL may bedetermined based on the variables dYInt[x] and dY[x][y].

For example, the variables dYInt[x] and dY[x][y] may be determinedaccording to Eq. 209-Eq. 210.dY Int[x]=((x+1)×invAngle+128)>>8  (Eq. 209)dY[x][y]=x+dY Int[x]  (Eq. 210)

Then, the reference samples refT[x][y], refL[x][y], and the weightingfactors wL, wT, and wTL may be determined according to Eq. 211-Eq. 215.refL[x][y]=(dY Int[y]<refH−height−1)?sideRef[dY[x][y]]: 0  (Eq. 211)refT[x][y]=0  (Eq. 212)wT[y]=0  (Eq. 213)wL[x]=32>>((x<<1)>>nScale)  (Eq. 214)wTL[x][y]=0  (Eq. 215)

Otherwise, when the variable preModeIntra is between modes 11-57 and isnot one of mode 18 and mode 50, then the reference samples refT[x][y,refL[x][y], and the weighting factors wL, wT, and wTL are all set equalto 0.

Finally, the values of the filtered samples filtSamples[x][y], with x=0. . . nTbW−1, y=0 . . . nTbH−1 may be derived according to Eq. 216:filtSamples[x][y]=clip1Cmp((refL[x][y]×wL+refT[x][y]×wT−p[−1][−1]×wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])×predSamples[x][y]+32)>>6)  (Eq. 216)

The difference between Embodiment C and Embodiment E is that inEmbodiment E, when the intra prediction mode preModeIntra is less thanor equal to INTRA_ANGULAR10, refT[x][y] may be calculated in a differentway (i.e., Eq. 125 vs. Eq. 205). Similarly, when the intra predictionmode preModeIntra is greater than or equal to INTRA_ANGULAR58,refL[x][y] may be calculated in a different way (i.e., Eq. 131 vs. Eq.211).

Early Termination of PDPC Process

According to embodiments of the disclosure, for intra prediction modesadjacent to the diagonal intra prediction modes, such as modes −1˜−14,modes 3˜10, modes 58˜65, and modes 67˜80 in FIG. 8A, the PDPC processcan have an early termination and the early termination depends on afractional position that the intra prediction direction is pointing onthe side reference samples which are used in the PDPC process.

In one embodiment, the assignment of reference sample value used in PDPCprocess is modified as follows.

For intra prediction modes adjacent to mode 2, Eq. 30 is modified as Eq.217.refT[x][y]=((dX[x][y]+(dXFrac[y]>>5))<refW−1)?mainRef[dX[x][y]+(dXFrac[y]>>5)]:0  (Eq.217)

For intra prediction modes adjacent to mode 66, Eq. 38 is modified asEq. 218.refL[x][y]=((dY[x][y]+(dXFrac[y]>>5))<refH−1)?sideRef[dY[x][y]+(dYFrac[x]>>5)]:0  (Eq.218)

Reference Sample Checking

In some related embodiments (e.g., in VVC), for a current sample in thePDPC process, a per-sample checking is needed to determine whether areference sample of the current sample is within a specified range. Ifthe reference sample is not within the specified range, the PDPCweighting factors are set to 0 for the current sample, as described in,for example, Eq. 30, Eq. 31, Eq. 38, and Eq. 41. However, thisper-sample checking may not be desired, especially for softwareoptimization using single instruction multiple data (SIMD) techniques.

According to some embodiments, the per-sample checking in the PDPCprocess, which is used to determine whether a reference sample is withinthe range of available reference samples, is replaced by a per-row orper-column checking. In an embodiment, the checking condition onlydepends on the number of available left reference samples, theprediction block height, and the horizontal coordinate value of thecurrent sample to be filtered by the PDPC process. In anotherembodiment, the checking condition only depends on the number ofavailable top reference samples, the prediction block width, and thevertical coordinate value of the current sample to be filtered by thePDPC process.

In an embodiment, for vertical-like intra prediction (i.e., a predictiondirection is closer to the vertical intra prediction direction than thehorizontal prediction direction), the checking is done per column, andthe checking condition only depends on at least one of the number ofavailable left reference samples, the prediction block height, and thehorizontal coordinate value of the current sample to be filtered by thePDPC process.

In an embodiment, for horizontal-like intra prediction (i.e., aprediction direction is closer to the horizontal intra predictiondirection than the vertical prediction direction), the checking is doneper row, and the checking condition only depends on at least one of thenumber of available top reference samples, the prediction block width,and the vertical coordinate value of the current sample to be filteredby the PDPC process.

According to some embodiments, the PDPC process is applied to an intraprediction mode when the intra prediction angle of the intra predictionmode is equal to or greater than a preset value, such as 2^(k)/32,wherein k is a non-negative integer, such as 3 or 4.

In an embodiment, for vertical-like intra prediction (i.e., a predictiondirection is closer to the vertical intra prediction direction otherthan the horizontal prediction direction), only the first(width/(2^(5-k))) (or min(width, height)/(2^(5-k))) columns of currentblock will be processed by the PDPC process.

In an embodiment, for horizontal-like intra prediction (i.e., aprediction direction is closer to horizontal intra prediction directionother than the vertical prediction direction), only the first(height/(2^(5-k))) (or min(width, height)/(2^(5-k))) rows of currentblock will be processed by the PDPC process.

FIG. 10 shows a flow chart outlining an exemplary process (1000)according to an embodiment of the disclosure. In various embodiments,the process (1000) is executed by processing circuitry, such as theprocessing circuitry in the terminal devices (210), (220), (230) and(240), the processing circuitry that performs functions of the videoencoder (303), the processing circuitry that performs functions of thevideo decoder (310), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the intra prediction module (452), the processing circuitrythat performs functions of the video encoder (503), the processingcircuitry that performs functions of the predictor (535), the processingcircuitry that performs functions of the intra encoder (622), theprocessing circuitry that performs functions of the intra decoder (772),and the like. In some embodiments, the process (1000) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(1000).

The process (1000) may generally start at step (S1010), where theprocess (1000) decodes prediction information for a current block in acurrent picture that is a part of a coded video sequence. The predictioninformation indicates an ultra prediction direction for the currentblock that is one of (i) a diagonal ultra prediction direction or (ii) aneighboring intra prediction direction adjacent to the diagonal intraprediction direction. Then the process (1000) proceeds to step (S1020).

At step (S1020), the process (1000) determines a usage of a positiondependent prediction combination (PDPC) process according to the intraprediction direction of the current block. The same PDPC process isapplied to both the diagonal intra prediction direction and theneighboring intra prediction direction. Then the process (1000) proceedsto step (S1030).

At step (S1030), the process (1000) reconstructs the current block basedon the usage of the PDPC process on the current block.

After reconstructing the current block, the process (1000) terminates.

In some embodiments, the diagonal intra prediction direction is one of abottom-left intra prediction direction and a top-right intra predictiondirection. In an embodiment, when the diagonal intra predictiondirection is the bottom-left intra prediction direction, a mode index ofthe neighboring intra prediction direction is below a mode index of ahorizontal intra prediction direction. In an embodiment, when thediagonal intra prediction direction is the top-right intra predictiondirection, the mode index of the neighboring intra prediction directionis above a mode index of a vertical intra prediction direction.

In an embodiment, when the intra prediction direction is the neighboringintra prediction direction, the process (1000) determines whether theintra prediction direction points to a fractional position. In responseto a determination that the intra prediction points to the fractionalposition, the process (1000) determines an early termination of the PDPCprocess.

In some embodiments, when a current sample in the current block is to befiltered by the PDPC process, the process (1000) determines whether areference sample of the current sample is located within a preset rangeaccording to a per-row or per-column checking. In an embodiment, theper-column checking depends on at least one of (i) a total number ofavailable reference samples that are located left to the current block,(ii) a block height of the current block, and (iii) a horizontalcoordinate value of the current sample. In an embodiment, the per-rowchecking depends on at least one of (i) a total number of availablereference samples that are located above the current block, (ii) a blockwidth of the current block, (iii) and a vertical coordinate value of thecurrent sample.

In some embodiments, an angle of the intra prediction direction is equalto or greater than a preset value. In an embodiment, when the intraprediction direction is closer to the vertical intra predictiondirection than the horizontal intra prediction direction, the process(1000) performs the PDPC process on a first number of columns of samplesin the current block, and the first number is determined according tothe preset value and a block size of the current block. In anembodiment, when the intra prediction direction is closer to thehorizontal intra prediction direction than the vertical intra predictiondirection, the process (1000) performs the PDPC process on a secondnumber of rows of samples in the current block, and the second number isdetermined according to the preset value and the block size of thecurrent block.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 11 shows a computersystem (1100) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computerscomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 11 for computer system (1100) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1100).

Computer system (1100) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1101), mouse (1102), trackpad (1103), touchscreen (1110), data-glove (not shown), joystick (1105), microphone(1106), scanner (1107), camera (1108).

Computer system (1100) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1110), data-glove (not shown), or joystick (1105), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1109), headphones(not depicted)), visual output devices (such as screens (1110) toinclude CRT screens, LCD screens, plasma screens, OILED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted). These visual output devices (such as screens(1110)) can be connected to a system bus (1148) through a graphicsadapter (1150).

Computer system (1100) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1120) with CD/DVD or the like media (1121), thumb-drive (1122),removable hard drive or solid state drive (1123), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1100) can also include a network interface (1154) toone or more communication networks (1155). The one or more communicationnetworks (1155) can for example be wireless, wireline, optical. The oneor more communication networks (1155) can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of the one or more communication networks (1155) includelocal area networks such as Ethernet, wireless LANs, cellular networksto include GSM, 3G, 4G, 5G, LTE and the like, TV wireline or wirelesswide area digital networks to include cable TV, satellite TV, andterrestrial broadcast TV, vehicular and industrial to include CANBus,and so forth. Certain networks commonly require external networkinterface adapters that attached to certain general purpose data portsor peripheral buses (1149) (such as, for example USB ports of thecomputer system (1100)); others are commonly integrated into the core ofthe computer system (1100) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1100) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1140) of thecomputer system (1100).

The core (1140) can include one or more Central Processing Units (CPU)(1141), Graphics Processing Units (GPU) (1142), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1143), hardware accelerators for certain tasks (1144), and so forth.These devices, along with Read-only memory (ROM) (1145), Random-accessmemory (1146), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1147), may be connectedthrough the system bus (1148). In some computer systems, the system bus(1148) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1148),or through a peripheral bus (1149). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1141), GPUs (1142), FPGAs (1143), and accelerators (1144) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1145) or RAM (1146). Transitional data can be also be stored in RAM(1146), whereas permanent data can be stored for example, in theinternal mass storage (1147). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1141), GPU (1142), massstorage (1147), ROM (1145), RAM (1146), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1100), and specifically the core (1140) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1140) that are of non-transitorynature, such as core-internal mass storage (1147) or ROM (1145). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1140). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1140) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1146) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1144)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods Which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

APPENDIX A: ACRONYMS

-   AMVP: Advanced Motion Vector Prediction-   ASIC: Application-Specific Integrated Circuit-   ATMVP: Alternative/Advanced Temporal Motion Vector Prediction-   BDOF: Bi-directional Optical Flow-   BIO: Bi-directional Optical Flow-   BMS: Benchmark Set-   BV: Block Vector-   CANBus: Controller Area Network Bus-   CB: Coding Block-   CBF: Coded Block Flag-   CCLM: Cross-Component Linear Mode/Model-   CD: Compact Disc-   CPR: Current Picture Referencing-   CPUs: Central Processing Units-   CRT: Cathode Ray Tube-   CTBs: Coding Tree Blocks-   CTUs: Coding Tree Units-   CU: Coding Unit-   DPB: Decoder Picture Buffer-   DVD: Digital Video Disc-   FPGA: Field Programmable Gate Areas-   GOPs: Groups of Pictures-   GPUs: Graphics Processing Units-   GSM: Global System for Mobile communications-   HDR: High Dynamic Range-   HEVC: High Efficiency Video Coding-   HRD: Hypothetical Reference Decoder-   Intra Block Copy-   IC: Integrated Circuit-   ISP: Intra Sub-Partitions-   JEM: Joint Exploration Model-   JVET: Joint Video Exploration Team-   LAN: Local Area Network-   LCD: Liquid-Crystal Display-   LTE: Long-Term Evolution-   MPM: Most Probable Mode-   MTS: Multiple Transform Selection-   MV: Motion Vector-   OLED: Organic Light-Emitting Diode-   PBs: Prediction. Blocks-   PCI: Peripheral Component Interconnect-   PD PC: Position Dependent Prediction Con Combination-   PLD: Programmable Logic Device-   PU: Prediction Unit-   RAM: Random Access Memory-   ROM: Read-Only Memory-   SBT: Sub-block Transform-   SCC: Screen Content Coding-   SDR: Standard Dynamic Range-   SEI: Supplementary Enhancement Information-   SNR: Signal Noise Ratio-   SSD: Solid-state Drive-   TUs: Transform Units-   USB: Universal Serial Bus-   VPDU: Visual Process Data Unit-   VUI Video Usability Information-   VVC: Versatile Video Coding-   WAIP: Wide-Angle Intra Prediction

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding prediction information for a current block in acurrent picture that is a part of a coded video sequence, the predictioninformation indicating an intra prediction direction for the currentblock that is one of (i) a diagonal intra prediction direction or (ii) aneighboring intra prediction direction adjacent to the diagonal intraprediction direction; determining a usage of a position dependentprediction combination (PDPC) process according to the intra predictiondirection of the current block, the same PDPC process being applied toboth the diagonal intra prediction direction and the neighboring intraprediction direction; and reconstructing, with the circuitry of thedecoder, the current block based on the usage of the PDPC process on thecurrent block, wherein based on the intra prediction direction beingcloser to a vertical intra prediction direction than a horizontal intraprediction direction, the PDPC process is performed on a first number ofcolumns of samples in the current block, and based on the intraprediction direction being closer to the horizontal intra predictiondirection than the vertical intra prediction direction, the PDPC processis performed on a second number of rows of samples in the current block.2. The method of claim 1, wherein the diagonal intra predictiondirection is one of a bottom-left ultra prediction direction and atop-right intra prediction direction.
 3. The method of claim 2, whereinwhen the diagonal intra prediction direction is the bottom-left intraprediction direction, a mode index of the neighboring intra predictiondirection is below a mode index of a horizontal intra predictiondirection.
 4. The method of claim 2, wherein when the diagonal intraprediction direction is the top-right intra prediction direction, a modeindex of the neighboring intra prediction direction is above a modeindex of a vertical intra prediction direction.
 5. The method of claim1, further comprising: when the intra prediction direction is theneighboring intra prediction direction, determining whether the intraprediction direction points to a fractional position; and determining anearly termination of the PDPC process in response to a determinationthat the intra prediction direction points to the fractional position.6. The method of claim 1, further comprising: when a current sample inthe current block is to be filtered by the PDPC process, determiningwhether a reference sample of the current sample is located within apreset range according to a per-row or per-column checking.
 7. Themethod of claim 6, wherein the per-column checking depends on at leastone of (i) a total number of available reference samples that arelocated left to the current block, (ii) a block height of the currentblock, and (iii) a horizontal coordinate value of the current sample. 8.The method of claim 6, wherein the per-row checking depends on at leastone of (i) a total number of available reference samples that arelocated above the current block, (ii) a block width of the currentblock, (iii) and a vertical coordinate value of the current sample. 9.The method of claim 1, wherein an angle of the intra predictiondirection is equal to or greater than a preset value.
 10. The method ofclaim 9, further comprising: the first number is determined according tothe preset value and a block size of the current block; and the secondnumber is determined according to the preset value and the block size ofthe current block.
 11. An apparatus, comprising a processing circuitryconfigured to: decode prediction information for a current block in acurrent picture that is a part of a coded video sequence, the predictioninformation indicating an intra prediction direction for the currentblock that is one of (i) a diagonal intra prediction direction or (ii) aneighboring intra prediction direction adjacent to the diagonal intraprediction direction; determine a usage of a position dependentprediction combination (PDPC) process according to the intra predictiondirection of the current block, the same PDPC process being applied toboth the diagonal intra prediction direction and the neighboring intraprediction direction; and reconstruct the current block based on theusage of the PDPC process on the current block, wherein based on theintra prediction direction being closer to a vertical intra predictiondirection than a horizontal intra prediction direction, the PDPC processis performed on a first number of columns of samples in the currentblock, and based on the intra prediction direction being closer to thehorizontal intra prediction direction than the vertical intra predictiondirection, the PDPC process is performed on a second number of rows ofsamples in the current block.
 12. The apparatus of claim 11, wherein thediagonal intra prediction direction is one of a bottom-left intraprediction direction and a top-right intra prediction direction.
 13. Theapparatus of claim 12, wherein when the diagonal intra predictiondirection is the bottom-left intra prediction direction, a mode index ofthe neighboring intra prediction direction is below a mode index of ahorizontal intra prediction direction.
 14. The apparatus of claim 12,wherein when the diagonal intra prediction direction is the top-rightintra prediction direction, the mode index of the neighboring intraprediction direction is above a mode index of a vertical intraprediction direction.
 15. The apparatus of claim 11, wherein theprocessing circuitry is further configured to: when the intra predictiondirection is the neighboring intra prediction direction, determinewhether the intra prediction direction points to a fractional position;and determine an early termination of the PDPC process in response to adetermination that the intra prediction points to the fractionalposition.
 16. The apparatus of claim 11, wherein the processingcircuitry is further configured to: when a current sample in the currentblock is to be filtered by the PDPC process, determine whether areference sample of the current sample is located within a preset rangeaccording to a per-row or per-column checking.
 17. The apparatus ofclaim 16, wherein the per-column checking depends on at least one of (i)a total number of available reference samples that are located left tothe current block, (ii) a block height of the current block, and (iii) ahorizontal coordinate value of the current sample.
 18. The apparatus ofclaim 16, wherein the per-row checking depends on at least one of (i) atotal number of available reference samples that are located above thecurrent block, (ii) a block width of the current block, (iii) and avertical coordinate value of the current sample.
 19. The apparatus ofclaim 11, wherein an angle of the intra prediction direction is equal toor greater than a preset value.
 20. A non-transitory computer-readablestorage medium storing a program that, when executed by at least oneprocessor, causes the at least one processor to perform a methodcomprising: decoding prediction information for a current block in acurrent picture that is a part of a coded video sequence, the predictioninformation indicating an intra prediction direction for the currentblock that is one of (i) a diagonal intra prediction direction or (ii) aneighboring intra prediction direction adjacent to the diagonal intraprediction direction; determining a usage of a position dependentprediction combination (PDPC) process according to the intra predictiondirection of the current block, the same PDPC process being applied toboth the diagonal intra prediction direction and the neighboring intraprediction direction; and reconstructing the current block based on theusage of the PDPC process on the current block, wherein based on theintra prediction direction being closer to a vertical intra predictiondirection than a horizontal intra prediction direction, the PDPC processis performed on a first number of columns of samples in the currentblock, and based on the intra prediction direction being closer to thehorizontal intra prediction direction than the vertical intra predictiondirection, the PDPC process is performed on a second number of rows ofsamples in the current block.